Joshua C. Thurow

The Kinematics of the Ionized Gas in IC 10

We present the results of a WIYN integral field unit study of the kinematics of the ionized gas in IC 10, a dwarf irregular starburst galaxy in the Local Group. Though the velocity field of the ionized gas closely matches that of the H I, there are several kinematically interesting features in the galaxy. The diffuse ionized gas in the galaxy exhibits larger Hα line widths than the bright complexes. In one case this is due to an infusion of energy into the gas associated with the radio superbubble discovered by Yang & Skillman. We find that the amount of energy in this region is consistent with their hypothesis that the region contains 10 supernova remnants. We also detect a high-velocity (70 km s-1) expanding shell in the ionized gas, which is likely driven by three confirmed Wolf-Rayet stars that are located within the shell. Extrapolating from Hunters initial mass function, we find that the central starburst region contains approximately equal energy contributions from stellar winds and supernovae (SNe), suggesting that SNe are just beginning to play a significant role in shaping the kinematics of the ionized gas. However, all of this energy cannot be easily accounted for in the kinematics of the gas. We detect an energetic flow of gas (3 × 1052 ergs), which we believe originates from the starburst region. We also detect a high-velocity (70 km s-1) feature not coincident with any structure in our Hα image. This feature, along with the flow and shell, can account for the energy produced by stellar wind and SNe. The flow resembles one discovered by Wilcots & Thurow in NGC 4214; together they suggest that the porosity of the interstellar medium contributes significantly to the high velocity of some portion of the ionized gas in irregular galaxies.

WIYN Integral Field Unit Study of the Kinematics of the Ionized Gas in NGC 4214

We present the results of a WIYN integral field unit study of the kinematics of the ionized gas in NGC 4214, a nearby Magellanic spiral that is forming copious numbers of massive stars. While there is general agreement between the Hα and H I velocity fields for NGC 4214, there are several regions where we find the velocities of the ionized gas to be 50-100 km s-1 higher than the H I velocities at those radii. The higher velocities are associated with the diffuse ionized gas, particularly in regions of low H I column density, and not with the discrete H II regions that are typically associated with H I clouds. The mechanical energy dumped into the interstellar medium of NGC 4214 by the combined stellar winds of the massive stars is more than sufficient to account for the kinematics of the ionized gas. The dearth of radio continuum sources argues that supernovae associated with the most recent burst of star formation have yet to shape the distribution and kinematics of the ionized (or neutral) gas in this galaxy. We suggest that the detected outflows of ionized gas are the result of windblown bubbles and expanding ionization fronts accelerating as they encounter the steep density gradients from H I clouds to H I holes.

The defeater version of Benacerraf's problem for a priori knowledge

Paul Benacerraf’s argument that mathematical realism is apparently incompatible with mathematical knowledge has been widely thought to also show that a priori knowledge in general is problematic. Although many philosophers have rejected Benacerraf’s argument because it assumes a causal theory of knowledge, some maintain that Benacerraf nevertheless put his finger on a genuine problem, even though he didn’t state the problem in its most challenging form. After diagnosing what went wrong with Benacerraf’s argument, I argue that a new, more challenging, version of Benacerraf’s problem can be constructed. The new version—what I call the Defeater Version—of Benacerraf’s problem makes use of a no-defeater condition on knowledge and justification. I conclude by arguing that the best way to avoid the problem is to construct a theory of how a priori judgments reliably track the facts. I also suggest four different kinds of theories worth pursuing.

Atoning in purgatory

This article develops a new argument – The Argument from Atonement – that commonplace Christian assumptions about heaven imply the existence of purgatory. According to this argument, many Christians will die with residual moral guilt due to possessing unfulfilled moral debts towards fellow non-divine humans. Some of these debts cannot be fulfilled immediately after death and are not completely fulfilled or cancelled by Jesuss atoning work. Christians with such debts are fit neither for heaven nor for hell and thus must occupy purgatory until their moral debts are fulfilled.